Metalorganic vapour phase epitaxy (MOVPE), also known as organometallic vapour phase epitaxy (OMVPE) or metalorganic chemical vapour deposition (MOCVD), is an arranged chemical vapour deposition method. In MOVPE ultra-pure gases are injected into a reactor and finely dosed to deposit a very thin layer of atoms onto a semiconductor wafer. Surface reaction of organic compounds or metalorganics and hydrides containing the required chemical elements creates conditions for crystalline growth—epitaxy of materials and compound semiconductors. Unlike traditional silicon semiconductors, these semiconductors may contain combinations of Group III and Group V, Group II and Group VI, Group IV, or Group IV, V and VI elements.
In the vapor phase epitaxy (VPE) technique, reactant gases are combined at elevated temperatures in the reactor to cause a chemical interaction, resulting in the deposition of materials on the substrate. In an atomic layer deposition (ALD) system, reactant gases are introduced sequentially to give self-limiting growth of conformal thin films of the desired materials. In both cases, the reactor is a chamber made of a material that does not react with the chemicals being used. It must also withstand high temperatures. This chamber comprises reactor walls, a liner, a susceptor, gas injection units, and temperature control units. Usually, the reactor walls are made from stainless steel or quartz. Ceramic or special glasses, such as quartz, are often used as the liner in the reactor chamber between the reactor wall and the susceptor. To prevent overheating, coolant, such as water, can flow through channels within the reactor walls. A substrate sits on a susceptor which is held at a controlled temperature. The susceptor is made from a material resistant to the metalorganic compounds used; graphite is sometimes used. For growing nitrides and related materials, a special coating on the graphite susceptor is necessary to prevent corrosion by ammonia (NH3) gas.
One type of reactor used to carry out MOCVD is a cold-wall reactor. In a cold-wall reactor, the substrate is supported by a pedestal, which also acts as a susceptor. The pedestal/susceptor is the primary origin of heat energy in the reaction chamber. Only the susceptor is heated, so gases do not react until they reach the hot wafer surface. The pedestal/susceptor is made of a radiation-absorbing material such as carbon. In contrast, the walls of the reaction chamber in a cold-wall reactor are typically made of quartz which is largely transparent to electromagnetic radiation. The reaction chamber walls in a cold-wall reactor may be indirectly heated by heat radiating from the hot pedestal/susceptor, but will remain cooler than the pedestal/susceptor and the substrate supported on the pedestal/susceptor.
In some situations, such as hot-wall CVD, the entire chamber is heated. This may be necessary for certain gases, which must be pre-cracked before reaching the substrate surface to allow them to stick to the substrate.
Gas is introduced to the reactor chamber via devices known as bubblers. In a bubbler a carrier gas (usually nitrogen or hydrogen) is bubbled through the metalorganic liquid, allowing the gas to pick up some metalorganic vapour and transport it to the reactor in the gas phase. The amount of metalorganic vapour transported depends on the rate of carrier gas flow, the bubbler temperature and the vapour pressure of the metalorganic precursor.
When thin film deposition is carried out, not only is the film deposited on the desired surface but also on all the interior surfaces of the MOCVD or ALD reactor including the susceptor, the walls and the ceiling. The more frequently the reactor is used without being cleaned, the thicker the deposits become. The deposits will eventually start to delaminate, generating particles that can fall onto the substrate wafers, contaminating them and resulting in either low yield or complete loss of the wafers. The reactant gases flowing through the reactor chamber may also be contaminated by the deposits. In order to avoid this, reactors must be cleaned out on a regular basis. Depending on the configurations and materials used in the reactor, effective cleaning may require complete reactor strip down and wet clean, which is time consuming and reduces reactor efficiency. In addition, a reactor is typically comprised of a wide range of materials such as 316L and 304 stainless steel, silicon carbide, graphite, tungsten, aluminum, pyrolytic boron nitride and/or ethylene propylene diene (EPDN) polymer. It can be difficult to clean deposits off all of these types of surfaces, without using different types of etchants or other cleaners. A simpler, more effective means of cleaning inside a reactor is therefore desired.
Dry HCl gas, HF gas or other reactive gas, together with a purge gas, may be used to remove certain deposits by dry etching. Upon contact with the reactive gas, the metal components are converted into volatile halides and removed with the purge gas. Use of these highly reactive etchants is difficult as they are corrosive to components within the reactor vessel and require high temperatures.
U.S. Publication No. 2009130860 to Miya et al. discloses a thermal etching technique for removing high dielectric constant films, such as hafnium, zirconium or aluminum oxides, from a reactor chamber. A halide-based etchant gas, such as BCl3, is supplied to the chamber, where the halide component is released, freeing the boron to preferentially bond with the oxygen from the deposited oxide film, breaking the chemical bonds within the deposited film. The reaction products may all then be purged from the reaction chamber. If a protective BxCly film forms over the film deposits, an oxygen-based component may be added to the etchant gas, which accelerates the etching reaction. Changing the temperature and pressure at which the etching reaction is carried out can also influence the etching rate. The etching procedure can take several cycles to satisfactorily remove the deposited film.
It is also known to clean MOCVD reactors using organic based materials. International Publication No. WO2011/117064 A1 to Hess et al. illustrates a method for deposition of multicomponent semiconductor layers, in particular III-V materials, onto a substrate located on a susceptor in a process chamber. Pyrolitic decomposition of one or more process gasses within the process chamber produces a deposition layer on the substrate and unwanted adherences to the surfaces of the process chamber. After or prior to deposition, the adherences are removed by introducing a purge gas containing a reactive substance comprising free radicals, preferably alkyl radicals or other hydrocarbon compounds, into the process chamber.
U.S. Publication No. 2004/0033310 to Sarigiannis et al. discloses a deposition method for depositing layers on a substrate while minimizing deposition on the internal walls of the reactor chamber. A process gas is introduced into a process chamber, where a substrate is carried by a heated susceptor. The process gas decomposes pyrolitically inside the heated process chamber. A layer is formed on the substrate and some material adheres to the process chamber surface. A reactive purge gas is provided to the deposition chamber, effectively forming a reactive gas curtain over the surfaces of the chamber walls, but away from the substrate. The adhering material reacts with the purge gas to form a volatile product which is then removed from the process chamber.
Alternatively, the components of the reactor vessel may be cleaned by wet etching, which involves dismantling of the vessel and then cleaning the components in suitable reagents. Wet etching is disadvantageous in that it is time and labour consuming in comparison with dry reactive gas etching.
Dry etching processes have been used in order to maximize deposition of preferred layer materials, and/or to better control the location of the deposition. For example, U.S. Pat. No. 5,326,431 to Kadomura discloses a dry etching method for Si or Al based substrate materials masked by a nitrogen based compound film such as TiON, Si3N4 or TiN, using an ionized etchant gas comprising a sulfur containing compound including SOF2, SOCl2, and SOBr2. The presence of sulfur compounds generates free sulfur which forms a protective layer on the masking layer, improving the anisotropy of the etching. The efficacy of the process may be improved by adding a halogen and/or a nitrogen based compound to the etchant gas.
U.S. Pat. No. 5,445,712 to Yanagida discloses a dry etching method for SiO2 based materials using an ionized etchant gas containing a fluorocarbon compound and an oxyhalogen compound such as carbonyl, thionyl, sulfuryl, nitrosyl, or nitryl halides. The oxyhalogen has the effect of extracting oxygen from SiO2, thereby increasing the etching of the silicon by the ionized fluorocarbon.
U.S. Pat. No. 5,378,653, also to Yanagida, describes a dry etching process for an Al-based metallization layer using an etchant gas having a halogen compound with a functional group, such as thionyl or sulfuryl, and a halogen atom. The etchant gas may also include a sulfur-based compound.
JP62280336 to Shoji discloses a method of recovering ruthenium from a base material of metallic oxides such as TiO2, Co2O3, Al2O3, SiO2, by crushing the mixture and heating it in the presence of carbon and a chloride gas such as COCl2, CCl4, or SOCl2. The base metal oxides form gaseous chlorides, which are removed by evaporation, while chlorides of Ru are dissociated by the high temperature allowing for the recovery of Ru metal from the residue by gravity separation.
These references generally detail a combination of multiple etchant mixtures and plasma to achieve the etching. Also the details in these references are quite specific, being directed to specific substrates and deposition materials.
It is therefore an object of the invention to provide a method of cleaning a reactor chamber that overcomes or minimizes the foregoing difficulties.
It is a further object of the invention to provide a low temperature, efficient method of cleaning a process chamber.
It is yet a further object of the invention to provide a method of cleaning a substrate prior to the deposition process.
A further object of the invention is to provide a method of etching masked layers on a substrate.
These and other objects of the invention will be appreciated by reference to the summary of the invention and to the detailed description of the preferred embodiment that follow.